Electric blasting cap



Get. 14, 1194? E. K. LEFREN ELECTRI C BLASTING CAP Filed April 1'7, 1942INVENTOR. EDWARD If. LEFREN 2,428,884 ELECTRIC BLASTING CAP Edward K.Lefren, Kingston, N. Y., assignor to Hercules Powder Company,Wilmington, DeL, a corporation of Delaware Application April 17, 1942,Serial No. 439,339 3 Claims. (Cl. 102-28) This invention relates toelectric blasting caps and electric firing devices and, moreparticularly, to a new and improved electric blasting cap which isprovided with means adapted to facilitate assembly of the parts in amoistureproof relationship.

lhe various prior art blasting devices such as electric blasting caps,electric delay caps, and the like, normally contain a plug which eitherslips loosely into the cap and is then sealed therein by means ofasphalt, or the like, or is sealed therein by means of crimping theshell into the plug itself. By these methods, caps can be mademoistureproof, but oftentimes due to temperature changes and variousexternal reasons, the caps do not maintain their moistureproofness. Inthe prior devices, the manufacture'of moistureproof caps is complicatedand time consuming. Each of the known caps in order to be'mademoistureproof requires a plurality of assembling operations.

The known caps which are supposedly waterproof are designed to includean explosive charge in the closed end of a bronze shell and an ignitionassembly adjacent to the explosive charge which consists of a pair oflead wires electrically connected by means of a resistance wire and heldin-position by means of a plug. This ignition assembly, in the majorityof instances, is inserted loosely into the cap' and sealing meanssuperimposed thereon. In some instances, the plug is inserted into thecap and the cap shell erimped into the plug.

The above described known methods of pro.- ducing moistureproof capshave met with commercial success but it has often been found that thecaps so produced do' not perform entirely satisfactorily since some fewof these caps may lack complete moistureproofness. The caps which do notremain moistureproof may cause trouble in firing various explosive shotsand are therefore undesirable. The moistureproofness of the caps may beseriously affected by hot storage conditions because moistureproofingmaterial such as asphalt tends to flow under a hot storage condition andeither to exude out of the top of the cap or leak past the plug downinto the explosive. Either type of flowage produces an unsatisfactorycap. In some instances, caps do not withstand cold storage because themoistureproofing agent may harden and become brittle and pull away fromthe shellunder low temperature conditions and thereby allow moisture toenter the shell. Prior art caps in which moistureproofing is effected bythe use of asphalt are undesirably long. Thdse in which the moistureresistance is produced by crimping the shell into the plug are somewhatshorter but the crimping operation isdiflicult to control and some typesof plugs must be heated to enable the shell to be crimped into the plug.

Therefore, it is an object of this invention to provide an electricblasting cap having a combination lock and sealing means adapted tofacilitate assembly of the cap and protect the cap against the entranceof moisture.

Another object is to provide a plug having resilient means adapted topermit quick assembly of the plug and shell, secure the plug inoperating position with the shell, and seal the shell against theentrance of moisture.

Nore specifically, it is an object to provide the plug of the ignitionassembly with spaced resilient fins adapted to facilitate assembly ofthe parts, secure the ignition assembly in operating position, and sealthe cap againstthe entrance of moisture.

Generally described, the electric blasting cap of the present inventioncomprises a shell preferably of copper, bronze, or aluminum having anexplosive charge in the closed end and having superimposed upon thisexplosive charge an ignition assembly comprising a dielectric plughaving a pair of leg wires therethrough in dielectric relation with oneanother, and a'resistance wire electrically connecting the terminal endsof these leg wires. The ignition assembly plug is provided withresilient fin-like members sufiiciently larger than the inside diameterof the blasting cap shell so that when the assembly is moved tooperating position with the shell, the members are compressed againstthe inner surface of the shell thereby forming a barrier against theentrance of moisture into the shell. The fin-like members are also bentupwardly out of normal alignment and in this position act as a lockingmeans for holding the assembly in operating position within the shell.

A preferred embodiment of the invention has been chosen for purposes ofillustration and de ing cap comprising an ignition assembly I and ablasting cap shell 2. The ignition assembly I comprises a pair ofinsulated leg wires 3 molded or otherwise inserted into a body portionof plug 4 each of which terminates at the lower end of the plu to form aterminal member or wire 5. These terminal wires are electricallyconnected by means of a bridge wire 6. The plug 4 may be made of rubber,resin, or any other suitable hard or soft dielectric material.

A combination moisture seal and locking means 7 in the form of fins Iare carried by the plug 4. These fins may be cast as an integral part ofthe plug 4 or may be separate units secured in any suitable mannerthereto. Where the plug 4 is made of a. rubber material, it is preferredto cast the fins and plug as an integral unit. Where the plug is made ofa hard material as, for example, a thermoplastic or thermosetting resin,it is preferred to make the fins in separate units of any suitableresilient material and then secure these units on the plug in anyconvenient manner as by cementing. v

The fins are formed with a substantially brcad base tapering outwardlytherefrom toward a relatively narrow rim portion. Formed in this manner,the fins are more resilient in their peripheral portion than at theirbase portion and in this way act to provide the desired moisture sealand locking effects.

The lower portion of the shell 2 is provided with an explosive chargewhich may comprise a base charge 8 and a priming charg 9. The basecharge 8 may be tetryl, pentaerythritol-tetranitrate, nitrostarch or thelike and the priming charge may be lead azide, diazo-dinitrophenol,mercury fulminate or the like either alone or admixed with an oxidizingagent such as potassium chlorate, barium nitrate, lead dioxide or thelike. The priming charge 9 is placed in the cap in a loose condition sothat the bridge wire 6 may be easily moved into the charge as the plugis positioned in the shell. This invention is applicable to capscontaining any arrangement of explosive charge, for example, singlecharge, or charges with ignition mixtures superimposed thereon.

The upper end of the shell, which is shown slightly greater in diameterthan the lower end, but which may be straight sided (not shown) ifdesirable, receives the plug together with the fins in tight fittingrelationship. As the plug 4 is moved into the shell, the fins I whichare diametrically larger than the inside diameter of the upper end ofthe shell, are compressed inwardly and moved upwardly out of normalalignment. After the plug has been moved into the position shown in Fig.2, the fins operate to provide a barrier against the entrance ofmoisture into the shell. The fins also act to lock the ignitionassemblyin operative position by reason of the fact that in' addition to thenormal tight fitting relationship between the fins and shell, the finstend to move into normal alignment during any outward movement of theplug which movement causes still greater compression of the fins andtherefore effects a still tighter fit between the fins and the shellwhich tighter fit then tends to prevent this outward movement of theplug relative to the shell.

Other ignition assemblies operable in accordance with this invention arethose of the cavity type, the bead type or the match head type.

The fins 1 may be modified to produce a locking and moisture sealingeflect. For example, a continuous helix may extend from the lower end ofthe body portion 4 to the upper end thereof and terminate in a sealingmember similar to the upper fin shown in the drawings. The fins may beperipherally-disposed about the body portion 4 out of horizontalalignment and the desired looking and sealing results obtained. Othermodifications are obvious from this disclosure.

From the foregoing description, it will be obvious that the objects ofthis invention have been accomplished by providing a blasting cap whichis simple, efiicient and economical to manufacture, which is providedwith means adapted to facilitate assembly of the parts, to provide amoisture seal and lock the parts in operating position.

What I claim and desire to protect by Letters Patent is:

1. An electric blasting cap which comprises a loaded tubular shellhaving a. dielectric ignition assembly plug disposed therein comprisinga body portion having a pair of leg wires extendin in spaced dielectricrelationship therethrough with the terminal ends of said pair of legwires extending from said body portion being connected by a bridge wire,and at least one resilient finl ke member outwardly and peripherallydisposed about said body portion, said finlike member being formed witha relatively broad base portion adjacent to said body portion andtapering outwardly therefrom toward a relatively narrow peripheralportion more resilient than said base and body portions, said peripheralportion being diametrically larger than the inside diameter of the upperend of said tubular shell prior to insertion into the shell.

2. An electric blasting cap which comprises a loaded tubular shellhaving a dielectric ignition assembly plug disposed therein comprising aresilient body portion having a pair of leg wires extending in spaceddielectric relationship therethrough with the terminal ends of said pairof leg Wires extending from said body portion being connected by abridge wire, and at least one resilient finlike member outwardly andperipherally disposed about said body portion, said finlike member beingformed with a relatively broad base portion adjacent to said bodyportion and tapering outwardly therefrom toward a relatively narrowperipheral portion more resilient than said base and body portions, saidperipheral portion being diametrically larger than the inside diameterof the upper end of said tubular shell prior to insertion into theshell.

3. An electric blasting cap which comprises a loaded tubular shellhaving a dielectric ignition assembly plug disposed therein comprising aresilient body portion having a pair of leg wires extending in spaceddielectric relationship therethrough with the terminal ends of said pairof leg wires extending from said body portion being connected by abridge wire, and a plurality of resilient finlike members outwardly andperipherally disposed about said body portion and in spaced parallelrelationship with each other, said finlike members being formed with arelatively broad base portion adjacent to said body portion and taperingoutwardly therefrom toward a relatively narrow peripheral portion moreresilient than said base and body portions,-said peripheral portionbeing diametrically larger than the inside diameter of the upper end ofsaid tubular shell prior to insertion into the shell.

EDWARD K.

REFERENCES @ITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Number Switzerland July 4, 1906

